This invention concerns a method to carry out bends and the relative device.
This invention is applied correctly to the field of the simultaneous processing of a plurality of bars for building work, whether those bars are obtained as sheared lengths or from coiled rolls, and advantageously to the processing of round, ribbed or shaped bars having a nominal diameter up to 32 mm.
The invention is applied advantageously, but not only, to bending machines having a horizontal platform of the type disclosed in EP-A-0.501.212 in the name of the same applicants.
The bending machines to which this invention is applied are normally employed to bend in four directions bundles of bars superimposed vertically, one bar on another, so as to produce geometric shapes which can be used in building work as reinforcement stirrups for reinforced concrete.
Such bending machines are disclosed, as regards their substantial components, in EP-A-0.501.212 and may have, or not have, an upstream store for bars.
These machines comprise a bending unit which may be of a rocking type (see EP-A-0.379.029) or of an orientable type (see EP-A-0.386.457) or of another type suitable for the purpose.
Means to retain and clamp a bundle of bars superimposed vertically are included advantageously together with the bending unit, as taught in EP-A-0.501.212, and are located immediately upstream and immediately downstream of the bending unit.
One or more lifting arms may cooperate with the bending unit, as in EP-A-0.502.341.
The retaining and clamping means act as abutment elements during the bending step and also as means to align and clamp the bundle of bars in position.
The retaining and clamping means of the state of the art have a first working position, in which they protrude from the work platform to clamp the bundle of bars to be bent, and a second retracted position in which they are located below the work platform so as not to contact the bundle of bars during the step of displacing and positioning the bundle.
A drawing unit cooperates with the bending unit, as is disclosed in EP-A-0.501.212. This drawing unit may also consist of rolls or tracked means located upstream and/or downstream of the bending unit so as to obtain a controlled lengthwise displacement of the bundle of bars.
Various problems which have to be overcome are entailed with this type of machine. A first problem is linked to the dimensional inaccuracies that distinguish the bars leaving the rolling step. These inaccuracies may vary even along the length of one and the same bar and are distinguished by a geometric shape different from the nominal shape; for instance, more or less oval shapes are often to be found on round bars.
Another problem consists in the lengthwise tensions which build up in the bar during the rolling, coiling and uncoiling steps; the straightening step is not always able to fix these tensions in a stable manner.
The tensions, if they are not fixed in the bar during the straightening step, are released in the bending step, so that the geometric figure produced becomes positioned on different planes at an angle to each other.
The final outcome of this is the production of reinforcement stirrups having a geometric conformation which is not level and therefore not suitable for use.
Another important problem is connected to the need to keep the bars of the bundle vertically superimposed on each other so that they can be engaged, clamped, guided and positioned correctly.
The falling of one or more bars prevents the retaining and clamping means from clamping the bars in the correct superimposed positions, from holding them correctly positioned in an identical manner and therefore from obtaining the same figures with the bars forming the same bundle.
Attempts are made at the present time to overcome this problem by guiding the sliding bundle of bars laterally by means of the bending unit itself by placing the bars in contact with the suitably positioned bending pin and abutment roll so as to define a passage having a width substantially almost the same as the diameter of the bars being displaced lengthwise.
This solution entails a great lengthening of the times of the cycle owing to the required positioning or re-positioning of the bending unit for each bend. Moreover, this system is not always able to overcome the problem since the bars which have fallen do not always rise into position again, and moreover it is not always possible to adopt this contrivance.
These problems linked to the high speed of bending and displacing the bundle of bars do not allow identical stirrups for reinforced concrete to be produced from bars in the same bundle.
Furthermore, it often happens that bundles of bars on which processing has started have to be discarded because the bars become entangled with each other.
Besides, stirrups which are not level or not correct may be found in one and the same bundle of stirrups.
FR-A-2.472.523 discloses a bending machine which includes means to butt and displace the bars lengthwise; these means consist of a thrust block, which is thrust against the rear end of the bars so as to make the front end of the bars cooperate with a resilient thrust abutment stop able to move lengthwise. So as to ensure lateral guiding, the bars are held in a U-shaped guide, which is open at its upper side and positioned upstream of the bending unit.
This bending machine entails a plurality of drawbacks including incorrect butting of the bars, inasmuch as the length of the bars is not always constant and is subject to the tolerances used in shearing the bars to size.
Moreover, the bending machine disclosed in this document requires replacement of the U-shaped guide whenever the diameter of the bars being processed is changed, so as to ensure correct vertical alignment of the bundle of bars. Furthermore, the inclusion of bars not having a constant diameter makes the solution of this document unacceptable for modern rates of output.
Besides, in the machine of this document of the state of the art the bundle of bars in the bending step is not clamped at its end opposite to the end at which the bend is made, and this situation may lead to bends which are not the same in bars of the same bundle.
Moreover, the bending machine of this document enables bends to be made only downstream of the bending unit and only in one direction, whether clockwise or anti-clockwise, and thus restricts considerably the number of figures which can be produced.
Furthermore, the machine of this document includes containing means which have the purpose of preventing the bundle of bars from being lifted from the work platform. The containing means disclosed are of a static type and consist of two stationary plates fitted to the thrust block and abutment stop respectively. These plates are installed in a stationary manner at a pre-set distance from the work platform and therefore have to be replaced from time to time to be suitable for the height of the bundle of bars being processed.
Besides, these plates have only one working position and therefore are always in contact or substantially in contact with the highest bar of the bundle of bars, and the plate associated with the abutment stop creates friction during the bending step.
Moreover, the thrust block and the plate associated with the thrust block have to have dimensions such that they can cooperate with the bars held in the U-shaped guide and therefore have to be replaced when the diameter of the bars being processed is changed.